This invention relates to the field of optoelectronic devices, and more particularly, to wavelength selective optoelectronic detectors.
Optoelectronic devices have found widespread use in telecommunications, medical, manufacturing and many other fields. Semiconductor lasers, semiconductor photo diodes, semiconductor photo detectors, etc., are all used in a wide variety of applications. In many applications, it is desirable for a detector to only detect selected optical signals. For example, in an application where the detector is exposed to a noisy optical environment, it may be desirable for the detector to only detect a narrow spectrum of light produced by a selected optical source like an LED or laser. That is, it can be desirable for a detector to be able to select an intended optical signal from the various optical signals present in the environment. Such a wavelength selective detector may help minimize the interference caused by unintended radiation sources.
In some applications, such as Wavelength Division Multiplexing (WDM) applications, it is desirable for the detector to be able to select a single wavelength from a number of signals that have closely spaced wavelengths. Such a wavelength selective detector may help increase the effective bandwidth of some fiber optic data channels.
Existing techniques for making wavelength-selective detectors include resonantcavity detectors, as well as assemblies that include, for example, one or more bandpass filters coupled together with a broad-band detector. However, these techniques often have significant drawbacks including, for example, high manufacturing costs and/or significant performance limitations.
The present invention provides a wavelength selective detector for detecting a desired wavelength or range of wavelengths of light. The wavelength selective detector of the present invention provides good out-of-band rejection, narrow spectral responsivity, and high in-band responsivity. In addition, the wavelength selective detector of the present invention is relatively easy to manufacture using conventional integrated circuit and compound semiconductor epitaxy fabrication techniques.
In one illustrative embodiment of the present invention, the wavelength selective detector includes a first absorbing layer for absorbing light that has a wavelength below the desired wavelength or range of wavelengths. Thus, the first absorbing layer may establish the lower cutoff of the wavelength selective detector. Tailoring the first absorbing layer to absorb wavelengths that are below the desired wavelength or range of wavelengths may be accomplished in any number of ways, including for example, using a material or material system that has an appropriate bandgap as well as adjusting the thickness of the first absorbing layer. The first absorbing layer may generate one or more carriers when absorbing light.
A second absorbing layer may be provided downstream of the first absorbing layer. The second absorbing layer preferably absorbs light that has the desired wavelength or range of wavelengths. Thus, the second absorbing layer may establish the upper cutoff of the wavelength selective detector. Again, this may be accomplished in any number of ways, including for example, using a material or material system that has an appropriate bandgap as well as adjusting the thickness of the second absorbing layer. Like the first absorbing layer, the second absorbing layer may also generate one or more carriers when the second absorbing layer absorbs light. A PN junction is preferably provided in or adjacent to the second absorbing layer for separating the carriers that are generated in the second absorbing layer, and to provide the output current for the detector.
To help prevent the carriers that are generated in the first absorbing layer from entering and affecting the output current of the detector (i.e. in the second absorbing layer), a confinement layer may be provided between the first absorbing layer and the second absorbing layer. To accomplish this, the confinement layer may, for example, have a higher bandgap than the first absorbing layer. The confinement layer preferably is at least substantially transparent to the desired wavelength or range of wavelengths of interest. To accomplish this, the confinement layer may, for example, have a higher bandgap than the second absorbing layer.
In some embodiments, the above detector is formed on a substrate. Light having a wavelength that is longer than the desired wavelength or range of wavelengths may pass through the first absorbing layer, the confinement layer, and the second absorbing layer before it is absorbed by the substrate. Some of the light may pass through the substrate altogether. In any event, to help prevent carriers that are generated in the substrate from entering and affecting the output current of the detector (e.g. in the second absorbing layer), a second confinement layer may be provided between the second absorbing layer and the substrate. The second confinement layer preferably is at least substantially transparent to wavelengths that are longer than the desired wavelength or range of wavelengths.